Hoover Dam

Year:1936

Duration:5 years

Cost:$49m

Country: USA

What did this project achieve?

Control water supply in order to provide for growing populations and farmland

The Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River. The construction was a huge undertaking involving the creation of several temporary towns to house thousands of workers. Construction began in early 1931.

The dam was constructed so that it is 200m thick at the bottom and only 14m near the top. The vast weight of water is held back by a curved face that transmits the water's force into the rock walls of the canyon, preventing its collapse.

Because of dangerous conditions and working practices at that time over 100 lives were lost during the build. Such a large concrete structure had never been built before and some of the methods the engineers used were completely new and untried.

This incredibly ambitious project was complicated by a summer of record-breaking high temperatures and difficulties with maintaining the workforce. However the dam was finished more than two years ahead of schedule.

Generators at the Hoover Dam produce over 2,000 megawatts of power. <a href="https://commons.wikimedia.org/wiki/File:Hoover_Dam%27s_generators2.jpg" target"_blank">Wikipedia</a>

Generators at the Hoover Dam produce over 2,000 megawatts of power. Wikipedia

Difference the project has made

Settlements in the US states of Arizona and California were growing fast and there was a big need for water and power. Controlling the river would also prevent floods and create a reservoir for irrigation of crops.

Today the dam's (new) generators provide power for Nevada, Arizona, and California. The Hoover Dam is also now a major tourist attraction with around a million visitors a year.

How the dam was built

Before the dam could be built the engineers had to divert the Colorado River away from the build site.

They did this by digging four 17m diameter, 1km long tunnels through the canyon walls and lining the tunnels with concrete. The river was then diverted into the two Arizona direction tunnels (the ones going towards Nevada were in reserve in case of high water).

Construction using such a huge amount of concrete posed some big challenges. The engineers realised that the massive amount of concrete being poured would take too long to cool and set, causing cracking so they had to come up with a solution. Their ingenious fix was to design a supersized fridge machine producing more than a thousand tonnes of ice every day to incorporate into the concrete.

To make sure the sides of the canyon would bear the pressure of the trapped lake, the side walls of the dam site had to be excavated of weathered rock. This was a huge and extremely dangerous task which was carried out by men known on site as ‘high scalers’.

Suspended from the top of the canyon by ropes, they climbed down the 200m walls to remove loose rock with jackhammers and dynamite.

The rock foundation underneath was reinforced with grout – called a grout curtain – and large, deep holes were drilled (up to 46m) and filled with more cement grout in order to fill any hidden cavities.

“​‌

This morning I came, I saw, and I was conquered, as everyone would be who sees for the first time this great feat of mankind. Ten years ago the place where we gathered was an unpeopled, forbidding desert. In the bottom of the gloomy canyon whose precipitous walls rose to a height of more than 1,000ft, flowed a turbulent, dangerous river. The transformation here in these years is a 20th century marvel.

Franklin D. Roosevelt

US President 1933-45

Fascinating facts

5m barrels of cement were used to build the dam

The dam holds 2.5m m3 of water in the form of Lake Mead which when full is the biggest reservoir in the US.

It produces an average of 4.5bn KW hours a year – powering 8m homes.

High scalers working on the dam invented the hard hat by dipping cloth hats in tar. The construction authorities liked this invention so much they ordered several thousand for other workers on the project.

People who made it happen

  • Chief design engineer: John L Savage
  • Six Companies consortium

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